Thermoplastic elastomer compositions produced by so called dynamic crosslinking, i.e. crosslinking of a radical crosslinkable, olefinic elastomer with a non-radical crosslinkable olefinic resin such as polypropylene (PP), etc. in the presence of a radical initiator, while melt-kneading them through an extruder belongs to the well known art and have been already widely used in automobile parts, etc.
For the thermoplastic elastomer compositions, ethylene-propylene-diene rubber (EPDM) has been so far used as an olefinic elastomer, where the diene component in the polymer chain is necessary for improving the crosslinkability, but the elastomer is not satisfactory yet with respect to the environment-caused deterioration resistance due to the diene component and their quality improvement has been keenly desired.
JP-A-8-120127 and JP-A-9-137001 disclose the art of using olefinic elastomers produced in the presence of a metallocene catalyst, but the elastomers are not satisfactory yet with respect to the quality and improvement of its quality has been desired.
An object of the present invention is to improve the processability and the environment-caused deterioration resistance, which have been problems of the conventional olefinic elastomers, and to provide an olefinic thermoplastic elastomer composition having distinguished mechanical characteristics, particularly a composition capable of having a low hardness and substantially free from such problems as oil bleed, etc.